In a display device having a backlight such as a liquid crystal display device, by performing brightness control of the backlight in accordance with an input image, power consumption of the backlight can be reduced. By performing, on the input image, gradation conversion which compensates a drop amount of the brightness of the backlight together with the brightness control of the backlight, while displaying an image similar to that of the case where the brightness control is not performed, power consumption of the backlight can be reduced.
There are the following methods of performing the brightness control of a backlight and the gradation conversion of an image. In a first method, a histogram of an input image is generated, a gradation in a position of a predetermined ratio (for example, a position of 90%) from a smaller side of the gradations of pixels included in the input image is obtained, and all of gradations larger than the obtained gradation are converted to a maximum gradation. In a second method, a data distribution or the like is analyzed based on a histogram of an input image and, according to an analysis result, a γ value of a γ curve is switched (for example, the γ value is switched from 2.2 to 1.8).
Patent document 1 describes an image display device having: means that detects the maximum value of image signals in one screen; light-transmission-type display means whose light transmittance becomes constant at the detected maximum value; and a light source obtaining a light output proportional to the detected maximum value. Patent document 2 describes an image adjusting method of applying a predetermined gain to a gradation smaller than a maximum faithful reproduction gradation and applying, to a gradation larger than the maximum faithful reproduction gradation, a roll-off curve using the maximum value of the gradation as a final reach point. Patent document 3 describes an image display method of obtaining a characteristic determination amount from display data and performing brightness conversion by applying a gain which changes before and after the characteristic determination amount. Patent document 4 describes a display device which controls intensity of light from a light source incoming to a light modulation display unit in accordance with an image to be displayed.    [Patent document 1] Japanese Laid-Open Patent Publication No. Hei 01-239589    [Patent document 2] Japanese Laid-Open Patent Publication No. 2006-293328    [Patent document 3] Japanese Laid-Open Patent Publication No. 2004-54250    [Patent document 4] U.S. Pat. No. 5,717,422